Firing one coil fires others too.

Two or more coils fire together

Cause: Solder shorts on the driver board, a bad 74LS374 latch, or the drive wires of two coils shorted together under the playfield.

Checks

• Inspect the driver board for solder bridges.
• Look for touching coil wires under the playfield.
• Check the latch for those coils.

Fix

• Clear the short or replace the latch.

Systems

• WPC Alpha-Numeric
• WPC Dot Matrix
• WPC Fliptronics
• WPC DCS
• WPC-Security (WPC-S)
• WPC-95

Related tips

• No 50 V coils work
• One coil will not fire
• Firing each coil from the WPC solenoid test
• A solenoid will not fire in the solenoid test
• A coil does nothing although its fuse is good
• Coil-not-working checklist
• Grounding test for WPC coils 1-8
• Checking the coil supply at TP6

Source: Repairing Williams/Bally WPC Pinball Games from 1990 to 1999, Part One, Clay Harrell (pinrepair.com)